The present invention generally relates to an image reading apparatus, and more particularly, to an image reading apparatus provided with an enlarging or magnifying function.
Commonly, in a digital copying apparatus, digital color copying apparatus or the like, enlargement is an essential function indispensable thereto. Accordingly, an image reading arrangement for transmitting binary-coded data of an image to a digital copying apparatus, etc., is required to be provided with an enlarging or magnifying function.
The enlarging or magnifying system for the image reading arrangement may be broadly divided into an optical magnifying type and an electrical magnifying type. In the optical magnifying type, the optical system is provided with a zoom function so as to read the image through enlarging of an image of the original document incident upon an image pickup element, while in the electrical magnifying type, the data read at a fixed magnification (fixed resolution) is processed.
In the variation of magnification through electrical processing, it is possible in principle to adopt any desired magnification, without limitations in the upper or lower limit value thereof. In the magnification variation, particularly in the direction of enlarging, however, deterioration of images tends to take place, since data which is not read originally must be prepared in a pseudo practice. On the other hand, in the variation of magnification by the optical system, it may be regarded that deterioration of the image quality is almost nil, and accordingly, upon comparison of the optical magnifying with the electrical magnifying, the optical magnifying is advantageous in terms of image quality.
Meanwhile, a disadvantage in the adoption of the optical magnifying is that there may be formed portions which can not be read on the original document as described hereinbelow.
FIGS. 11(a) and 11(b) respectively show the relation between an original document and a CCD (charge coupled device) surface during an equal size or life size magnification and during enlargement. In the equal size magnification, the image on the entire surface of the original document (in a main scanning direction) is projected over the CCD surface as shown in FIG. 11(a), whereas during the enlarging, the image on the entire surface of the original document is not projected over the CCD surface as illustrated in FIG. 11(b). In other words, regions M and M' at opposite edges on the surface of the original document can not be read.
In the general enlarging operation (e.g., conversion from an A5 size original document into A4 size), no inconvenience is experienced in many cases, even if such unreadable portions are present.
However, in the case where the original document is of a maximum size for equal size reading, with a partial enlarging being required to be effected, there are cases where the region aimed at enters the unreadable region M or M'.
In the conventional practice, when the state as described above takes place, there is no other way than to displace the original document into the readable region by an operator. For such an editing work, it is frequently required to designate the enlarged reading region after monitoring by a monitor device such as a CRT and the like subsequent to once reading the whole image surface at an equal size magnification, thus resulting in necessity for the operator to displace the original document depending on adopted magnifications and regions, or in obstruction against smooth operation. Particularly, in the case where an automatic document feeder is employed, it is impossible for the operator to displace the original document to its position.